1. Field of the Invention
In general, this invention is directed to a fire-resistant, essentially halogen-free epoxy composition that emits low amounts of smoke and toxic gas while burning. The one-part composition is particularly useful in aerospace applications for bonding, sealing and/or insulating metal, plastic and composite parts.
2. Description of the Related Art
U.S. Pat. No. 5,019,605 discloses a low density, self-extinguishing epoxide composition comprising:
(a) from 10 to 75 percent by weight of an organic epoxide compound having an epoxide functionality of at least 1; PA1 (b) from 1 to 25 percent by weight of an epoxide hardener; PA1 (c) from 20 to 50 percent by weight of a smoke suppressant; PA1 (d) from 10 to 25 percent by weight of a low density filler; and PA1 (e) from 1 to 10 percent by weight of an organic phosphorous-containing compound selected from the group consisting of alkyl phosphates, aryl phosphates, alkylphosphonates, arylphosphonates, and mixtures thereof. PA1 (i) a burn rate of less than 150 mm; PA1 (ii) a flame time of less than 15 seconds; and PA1 (iii) a drip flame time of less than 3 seconds. PA1 (a) 100 parts by weight of an organic epoxide compound having an epoxide functionality of at least 1; PA1 (b) from 2 to 180 parts by weight of an epoxide hardener; PA1 (c) from 0.5 to 40 parts by weight of a film-forming material; PA1 (d) from 0.5 to 30 parts by weight of a foaming agent; and PA1 (e) from 60 to 230 parts by weight of an essentially halogen-free fire-resistant system that includes: PA1 HF: less than 50 parts per million (ppm) after 1.5 minutes and 4 minutes; PA1 HCl: less than 50 ppm after 1.5 minutes and less than 500 ppm after 4 minutes; PA1 HCN: less than 100 ppm after 1.5 minutes and less than 150 ppm after 4 minutes; PA1 SO.sub.2 : less than 50 ppm after 1.5 minutes and less than 100 ppm after 4 minutes; PA1 CO: less than 3000 ppm after 1.5 minutes and less than 3500 ppm after 4 minutes; and PA1 NO+NO.sub.2 : less than 50 ppm after 1.5 minutes and less than 100 ppm after 4 minutes.
The self-extinguishing composition, which contains from 3 to 10 percent by weight bromine, also provides smoke suppression and has excellent compressive strength.
More specifically, the epoxide composition, after hardening, possesses (i) a non-flaming smoke density of less than about 100 after 90 seconds and less than about 200 after 240 seconds, and (ii) a flaming smoke density of less than about 100 after 90 seconds and less than about 200 after 240 seconds.
Other characteristics preferably demonstrated by the hardened epoxide compositions include:
The epoxide compositions were apparently developed to satisfy Airbus Technical Specification (ATS) 1000.001 (Chapter 7), third issue, October, 1980 and FAR 25853 (a) and (b). However, the stringency of these specifications was subsequently increased to require smoke densities that do not exceed 150. Moreover, the bromine-containing component is potentially toxic.
U.S. Pat. No. 4,145,369 discloses a flame-retardant epoxy composition comprising 100 parts by weight of a polyepoxide containing more than one epoxy group, 0.8 to 1.2 equivalents of an acid anhydride curing agent per equivalent of the polyepoxide, 0.5 to 5 parts by weight of an imidazole curing agent per 100 parts by weight of the polyepoxide, an aluminum trihydrate powder, and either red phosphorus powder or red phosphorus powder coated with a thermosetting resin. The appropriate amounts of these latter materials are determined with reference to the graph of FIG. 1.
U.S. Pat. No. 4,879,067 discloses a flame retardant of red phosphorus and a non-flammable resinous composition containing the same. The red phosphorous is provided as fine spherical particles free of pulverized angular faces. The particles can be coated with a thermosetting resin and/or a hydroxide of aluminum or zinc. A mixture of (i) an alkaline earth metal hydroxide or an aluminium group hydroxide, and (ii) a phosphorus-containing material is not disclosed.
There is a continuing need for flame retardant compositions that do not include brominated materials or other potentially toxic ingredients and that can readily satisfy the more recent and stringent ATS 1000 specification.